Suchergebnisse

Abstract. Consecutive ML 7.0 submarine earthquakes occurred offshore of the Hengchun Peninsula, Taiwan, on 26 December 2006. A small tsunami was generated and recorded at tide gauge stations. This important event attracted public interest, as it was generated by an earthquake doublet and produced a tsunami risk for Taiwan. This study analyzed tide gauge tsunami waveforms and numerical simulations to understand the source characteristics
and resulting behaviors of tsunamis. The maximum wave heights at the three
nearest stations were 0.08 m (Kaohsiung), 0.12 m (Dongkung), and 0.3 m
(Houbihu), and only Houbihu recorded the first wave crest as the largest.
The tsunami duration was 3.9 h at Dongkung and over 6 h at Kaohsiung and
Houbihu. Spectral analyses detected dominant periodic components of spectral peaks on the tsunami waveforms. The period band from 13.6–23.1 min was identified as the tsunami source spectrum, and the approximate fault area for the consecutive tsunamis was estimated to be 800 km2, with central fault depths of 20 km (first earthquake, Mw 7.0) and 33 km (second earthquake, Mw 6.9). The focal mechanisms of the first earthquake, with
a strike of 319∘, dip of 69∘, and rake of
−102∘, and the second earthquake, with a strike of 151∘, dip of 48∘, and rake of 0∘, could successfully
reproduce the observed tsunami waveforms. Numerical simulations suggested
that the tsunami waves were coastally trapped on the south coast of Taiwan
during the tsunami's passage. The trapped waves propagated along the coast
as edge waves, which repeatedly reflected and refracted among the shelves,
interfered with incoming incident wave, and resonated with the fundamental
modes of the shelves, amplifying and continuing the tsunami wave
oscillation. These results elucidated the generation and consequential
behaviors of the 2006 tsunami in southern Taiwan, contributing essential
information for tsunami warning and coastal emergency response in Taiwan to
reduce disaster risk.

Abstract. On 22 December 2018, a tsunami was generated from the Mount Anak Krakatau
area that was caused by volcanic flank failures. The tsunami had severe
impacts on the western coast of Banten and the southern coasts of Lampung in
Indonesia. A series of surveys to measure the impacts of the tsunami was
started 3 d after the tsunami and lasted for 10 d. Immediate
investigations allowed the collection of relatively authentic images of the
tsunami impacts before the clearing process started. This article
investigates the impacts of the 2018 Sunda Strait tsunami on the affected
areas and presents an analysis of the impacts of pure hydrodynamic tsunami
forces on buildings. Impacts of the tsunami were expected to exhibit
different characteristics than those found following the 2004 Indian Ocean
tsunami in Aceh. Data were collected from 117 flow depths along the Banten
and Lampung coasts. Furthermore, 98 buildings or houses were assessed for
damage. Results of this study revealed that the flow depths were higher in
Banten than in Lampung. Directions of the tsunami arrays created by the
complex bathymetry around the strait caused these differences.
Tsunami-induced damage to buildings was mostly the result of impact forces
and drag forces. Damping forces could not be associated with the damage.
The tsunami warning system in Indonesia should be extended to anticipate
non-seismic tsunamis, such as landslides and volcanic processes driven by
tsunamis. The lack of a tsunami warning during the first few minutes after the
generation of the first wave led to a significant number of human casualties
in both of the affected areas.

Abstract. This research aimed to assess the tsunami flow velocity and height reduction produced by a planned elevated road parallel to the coast of Banda Aceh, called the Banda Aceh Outer Ring Road (BORR). The road will transect several lagoons, settlements, and bare land around the coast of Banda Aceh. Beside its main function to reduce traffic congestion in the city, the BORR is also proposed to reduce the impacts of future tsunamis. The Cornell Multi-grid Coupled Tsunami Model (COMCOT) was used to simulate eight scenarios of the tsunami. One of them was based on the 2004 Indian Ocean tsunami. Two magnitudes of earthquake were used, that is, 8.5 and 9.15 Mw. Both the earthquakes were generated from the same source location as in the 2004 case, around the Andaman Sea. Land use data of the innermost layer of the simulation area were adopted based on the 2004 condition and the land use planning of the city for 2029. The results of this study reveal that the tsunami inundation area can be reduced by about 9 % by using the elevated road for the earthquake of magnitude 9.15 Mw and about 22 % for the earthquake of magnitude 8.5 Mw. Combined with the land use planning 2029, the elevated road could reduce the maximum flow velocities behind the road by about 72 %. Notably, the proposed land use for 2029 will not be sufficient to deliver any effects on the tsunami mitigation without the elevated road structures. We recommend the city to construct the elevated road as this could be part of the co-benefit structures for tsunami mitigation. The proposed BORR appears to deliver a significant reduction of impacts of the smaller intensity tsunamis compared to the 2004 Indian Ocean tsunami.

Abstract. The 2004 Indian Ocean tsunami and the 2011 Tōhoku earthquake and tsunami caused large-scale topographic changes in coastal areas. Whereas much research has focused on coastlines that have or had large human populations, little focus has been paid to coastlines that have little or no infrastructure. The importance of examining erosional and depositional mechanisms of tsunami events lies in the rapid reorganization that coastlines must undertake immediately after an event. A thorough understanding of the pre-event conditions is paramount to understanding the natural reconstruction of the coastal environment. This study examines the location of sediment erosion and deposition during the 2004 Indian Ocean tsunami event on the relatively pristine Phra Thong Island, Thailand. Coupled with satellite imagery, we use numerical simulations and sediment transportation models to determine the locations of significant erosion and the areas where much of that sediment was redeposited during the tsunami inundation and backwash processes. Our modeling approach suggests that beaches located in two regions on Phra Thong Island were significantly eroded by the 2004 tsunami, predominantly during the backwash phase of the first and largest wave to strike the island. Although 2004 tsunami deposits are found on the island, we demonstrate that most of the sediment was deposited in the shallow coastal area, facilitating quick recovery of the beach when normal coastal processes resumed.

Abstract. Since the two devastating tsunamis in 2004 (Indian Ocean) and 2011 (Great East Japan), new findings have emerged on the relationship between tsunami characteristics and damage in terms of fragility functions. Human loss and damage to buildings and infrastructures are the primary target of recovery and reconstruction; thus, such relationships for offshore properties and marine ecosystems remain unclear. To overcome this lack of knowledge, this study used the available data from two possible target areas (Mangokuura Lake and Matsushima Bay) from the 2011 Japan tsunami. This study has three main components: (1) reproduction of the 2011 tsunami, (2) damage investigation, and (3) fragility function development. First, the source models of the 2011 tsunami were verified and adjusted to reproduce the tsunami characteristics in the target areas. Second, the damage ratio (complete damage) of the aquaculture raft and eelgrass was investigated using satellite images taken before and after the 2011 tsunami through visual inspection and binarization. Third, the tsunami fragility functions were developed using the relationship between the simulated tsunami characteristics and the estimated damage ratio. Based on the statistical analysis results, fragility functions were developed for Mangokuura Lake, and the flow velocity was the main contributor to the damage instead of the wave amplitude. For example, the damage ratio above 0.9 was found to be equal to the maximum flow velocities of 1.3 m s−1 (aquaculture raft) and 3.0 m s−1 (eelgrass). This finding is consistent with the previously proposed damage criterion of 1 m s−1 for the aquaculture raft. This study is the first step in the development of damage assessment and planning for marine products and environmental factors to mitigate the effects of future tsunamis.

Abstract. This study proposes a framework for utilizing results obtained from advanced numerical simulations and performing probabilistic tsunami hazard assessment for investigating optimal facility placement. A set of numerical simulations of the tsunami off the Pacific coast caused by the 2011 Tohoku earthquake are performed considering uncertainties in fault parameters. Both inundation depths and tsunami forces acting on buildings are numerically simulated and defined as tsunami hazard indices. Proper orthogonal decomposition is then applied to numerical results for extracting characteristic spatial modes, which can be used to construct surrogate models. Monte Carlo simulations (MCSs) were performed at a low computational cost using surrogate models. The optimal placement of facilities was probabilistically investigated with the help of genetic algorithms using the MCS results along with the concept of system failure probability. The results indicate that the proposed framework allows determining the optimal placement of facilities by applying different strategies at low computational costs while effectively reflecting the results of advanced tsunami simulations.

Abstract. Indonesia has experienced several tsunamis triggered by seismic and non-seismic (i.e., landslides) sources. These events damaged or destroyed coastal buildings and infrastructure and caused considerable loss of life. Based on the Global Earthquake Model (GEM) guidelines, this study assesses the empirical tsunami fragility to the buildings inventory of the 2018 Sunda Strait, 2018 Sulawesi–Palu, and 2004 Indian Ocean (Khao Lak–Phuket, Thailand) tsunamis. Fragility curves represent the impact of tsunami characteristics on structural components and express the likelihood of a structure reaching or exceeding a damage state in response to a tsunami
intensity measure. The Sunda Strait and Sulawesi–Palu tsunamis are uncommon events still poorly understood compared to the Indian Ocean tsunami (IOT), and their post-tsunami databases include only flow depth values. Using the TUNAMI two-layer model, we thus reproduce the flow depth, the flow velocity, and the hydrodynamic force of these two tsunamis for the first time. The flow depth is found to be the best descriptor of tsunami damage for both events. Accordingly, the building fragility curves for complete damage reveal that (i) in Khao Lak–Phuket, the buildings affected by the IOT sustained more damage than the Sunda Strait tsunami, characterized by shorter wave periods, and (ii) the buildings performed better in Khao Lak–Phuket than in Banda Aceh (Indonesia). Although the IOT affected both locations, ground motions were recorded in the city of Banda Aceh, and buildings could have been seismically damaged prior to the tsunami's arrival, and (iii) the buildings of Palu City exposed to the Sulawesi–Palu tsunami were more susceptible to complete damage than the ones affected by the IOT, in Banda Aceh, between 0 and 2 m flow depth. Similar to the Banda Aceh case, the Sulawesi–Palu tsunami load may not be the only cause of structural destruction. The buildings' susceptibility to tsunami damage in the waterfront of Palu City could have been enhanced by liquefaction events triggered by the 2018 Sulawesi earthquake.

Abstract. Tsunami fragility functions describe the probability of structural damage due to tsunami flow characteristics. Fragility functions developed from past
tsunami events (e.g., the 2004 Indian Ocean tsunami) are often applied directly,
without modification, to other areas at risk of tsunami for the purpose of
damage and loss estimations. Consequentially, estimates carry uncertainty
due to disparities in construction standards and coastal morphology between
the specific region for which the fragility functions were originally
derived and the region where they are being used. The main objective of
this study is to provide an alternative approach to assessing tsunami
damage, especially for buildings in regions where previously developed
fragility functions do not exist. A damage assessment model is proposed in
this study, where load-resistance analysis is performed for each building by evaluating hydrodynamic forces, buoyancies and debris impacts and comparing them to the resistance forces of each building. Numerical simulation was performed in this study to reproduce the 2011 Great East Japan tsunami in Ishinomaki, which is chosen as a study site. Flow depths and velocities were calculated for approximately 20 000 wooden buildings in Ishinomaki. Similarly, resistance forces (lateral and vertical) are estimated for each of these buildings. The buildings are then evaluated for their potential of collapsing. Results from this study reflect a higher accuracy in predicting building collapse when using the proposed load-resistance analysis, as compared to previously developed fragility functions in the same study area. Damage is also observed to have likely occurred before flow depth and velocity reach maximum values. With the above considerations, the proposed damage model might well be an alternative for building damage assessments in areas that have yet to be affected by modern tsunami events.

Abstract. Modern tsunami events have highlighted the vulnerability of port structures to these high-impact but infrequent occurrences. However, port planning rarely includes adaptation measures to address tsunami hazards. The 2011 Tohoku tsunami presented us with an opportunity to characterise the
vulnerability of port industries to tsunami impacts. Here, we provide a
spatial assessment and photographic interpretation of freely available data
sources. Approximately 5000 port structures were assessed for damage and
stored in a database. Using the newly developed damage database, tsunami
damage is quantified statistically for the first time, through the development of damage fragility functions for eight common port industries.
In contrast to tsunami damage fragility functions produced for buildings
from an existing damage database, our fragility functions showed higher
prediction accuracies (up to 75 % accuracy). Pre-tsunami earthquake damage was also assessed in this study and was found to influence overall damage assessment. The damage database and fragility functions for port industries can inform structural improvements and mitigation plans for ports against future events.